1. Field of the Invention
The present invention generally relates to optical sheets, and particularly, to a prism sheet used in a liquid crystal display (LCD).
2. Discussion of the Related Art
FIG. 5 is an exploded, side cross-sectional view of a typical liquid crystal display device 100 employing a typical prism sheet 10. The liquid crystal display device 100 includes a housing 11 and a plurality of lamps 12 positioned in the housing 11. The liquid crystal display device 100 further includes a light diffusion plate 13, a prism sheet 10, and a LCD panel 15 stacked on the housing 11 in that order. The lamps 12 emit light, and inside walls of the housing 11 are configured for reflecting some of the light upwards. In use, light emitted from the lamps 12 enters the prism sheet 10 after scattered in the diffusion plate 13. The light is refracted and concentrated by the V-shaped protrusions 103 of the prism sheet 10, and then the light finally propagates into the liquid crystal display panel 15.
Referring to FIG. 6, the prism sheet 10 includes a base layer 101 and a prism layer 102 formed on the base layer 101. The prism layer 102 has a plurality of V-shaped protrusions 103. The V-shaped protrusions 103 are regularly arranged and extend along a direction parallel to one edge of the prism sheet 10. Typically, a method of manufacturing the prism sheet 10 includes following steps: first, a melted ultraviolet(UV)-cured transparent resin is coated on the base layer 101 to form V-shaped lenses, then the melted ultraviolet-cured transparent resin is solidified to form the prism layer 102. This results in that the V-shaped protrusions 103 of the prism layer 102 are easily damaged or scratched due to poor rigidity and mechanical strength.
However, the V-shaped protrusions 103 are prone to be aligned similarly to pixels of the liquid crystal display panel 15, consequently, moiré patterns may occur between the prism sheet 10 and the pixel pitch of the liquid crystal display panel 15. In order to reduce or eliminate the moiré patterns and protect the V-shaped protrusions 103 of the prism sheet 10, the liquid crystal display device 100 should further include an upper light diffusion film 14 on the prism sheet 10. However, although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets still exist at the boundary between the light diffusion film 14 and the prism sheet 10. When the liquid crystal display device 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection at one or another of the corresponding boundaries. In addition, the upper light diffusion film 14 may absorb an amount of the light from the prism sheet 10. As a result, a brightness of light illumination of the liquid crystal display device 100 is reduced.
Therefore, a new prism sheet is desired in order to overcome the above-described shortcomings.